As the baby boomer generation ages, the number of hip replacement surgeries is expected to increase. In 2001, about 165,000 hip joints were replaced in U.S. hospitals according to the National Center for Health Statistics, and 326,000 knees were replaced. While the majority of joint replacement patients remain in the 60-plus year category, more people are deciding to have surgery one or two decades earlier.
About 70 percent of people seeking hip replacement surgery have severe osteoarthritis, a common chronic disease that damages cartilage, a type of tissue that acts as a protective cushion allowing for the smooth, low-friction movement of the joint. Osteoarthritis is the leading cause of long-term knee damage and the most common reason for knee replacement. By age 65, women are five times more likely than men to have this disease.
A common goal for physicians when replacing joints is to minimize the discomfort and the recovery time, and reduce the time it takes to successfully install the joint implant while properly installing the new joint to provide the best possible range of motion for the patient using materials and techniques which will maximize the lifetime of the replacement joint. To this end, pre-surgery planning is an important step in the joint replacement process so that the surgeon is able to properly select the best joint replacement option and estimate how it will fit prior to the actual surgery.
Unfortunately, many current planning techniques rely on two-dimensional acetate portrayals of a prosthetic devise implanted which is then overlaid on the patient's two-dimensional x-ray. For example, for hip replacements, commonly used current planning methods for acetabular implant placement and size selection is performed using acetate templates and a single anterior-posterior x-ray of the pelvis. Acetabular templating is mostly performed to determine the approximate size of the acetabular component, but there is little effort to accurately determine the ideal position of the implant prior to surgery. Even implant selection for fit and fill with acetates can be problematic since the subject's x-ray may be rotated compared to the ideal view plane assumed when the acetate was created.
Discrepancies in implant size and placement which remain undetected during planning can lead to longer and more traumatic surgeries as originally intended prosthesis are removed and alternative prosthesis are used to correct mis-alignments which only become apparent after the operation has begun. Many discrepancies between the desired and actual implant placement can go unnoticed, possibly resulting in reduced range of motion, impingement and subsequent dislocation, or premature joint wear. For example, the incidence of dislocation following primary total hip replacement (THR) surgery is between 2-6% and even higher following revisions. It is, therefore, one of the most commonly occurring complications following hip replacement surgery. Dislocation of a total hip replacement causes significant distress to the patient and physician and is associated with significant additional costs in order to relocate the hip. Another complication of THR surgery is impingement between the neck of the femoral implant and the rim of the acetabular component. Impingement can lead to advanced wear of the acetabular rim resulting in polyethylene wear debris shown to accelerate loosening of implant bone interfaces. The position at which impingement occurs is determined by the design and geometry of the implants (such as the size of the femoral head, the width of the neck, and the design of the acetabular liner), and more importantly by the relative position of the femoral and acetabular implants. In certain cases, impingement may result in dislocation. Therefore, it is highly desirable to have a method and a system which more accurately enables physicians to plan for surgical joint replacement.
With the increasing use of computers in society, surgical planning solutions for joint replacement have been developed which will display a two-dimensional (2D) slice of a three-dimensional (3D) prosthetic on a 2D image. While this 2D slice can be scaled and rotated electronically, the physician is not assured of choosing the correct rotation or orientation.
Therefore, despite advances in computer planning software, there is still a need for methods and systems that more accurately enable physicians to plan.